In North America, asphalt-based roofing materials are a popular medium for covering roofs of homes and other structures. Asphalt-based roofing materials typically come in shingle or roll form, the shingle being the more widely used material. A typical asphalt shingle has an asphalt substrate and a multitude of granules placed thereon.
As energy prices have risen, the demand for energy efficient roof systems has increased. In certain communities, building codes have been issued to require more energy efficient buildings. Energy-efficient roofing materials can result in cooler roof surfaces and less energy spent to cool a building. As such, energy-efficient roofing materials can reduced building cooling costs. The use of energy efficient roof coatings can also reduce the amount of roof insulation required in a building.
Due to the demand of energy-efficient roofing materials, several roofing systems have been developed. One type of energy-efficient roofing material is disclosed in U.S. Pat. No. 6,933,007 discloses the use of reflective granules on a roofing material to form energy-efficient roofing materials. U.S. patent application Ser. No. 10/951,973 filed Sep. 29, 2004, which is incorporated herein by reference discloses a paint applied to a roofing material to form energy-efficient roofing materials.
Various types of acrylic coatings have been used on roofing materials to form energy-efficient roofing materials. For example, white, water-based acrylic coatings have been found to provide the highest reflectivity and longevity. White reflective coatings also typically minimize heat damage to roof membranes, increasing their expected service lives. Acrylic coatings primarily are formulated with pigments, acrylic polymers and water. There may be other additives, such as fibers for reinforcement, glycol for freeze thaw resistance, intumescant or other fire-retardant additives, or biocides to prevent fungal growth in the container. Historically, prior art white, water-based acrylic coatings have problems maintaining roof surface reflectivity. For instance, reflectivity can decrease significantly during the first year of a roofs life. Changes in reflectivity are related to changes with the coating itself (e.g., coating-erosion or cracking) and/or accumulation of particulate matter (e.g., dirt) from the environment.
Some prior art acrylic coatings have been applied directly to granule-surfaced modified bitumen roof membranes on new roof systems. Granules are difficult to coat because of their rough, uneven surface areas. Moisture and air pockets can be trapped under the acrylic coating and lead to blisters or pinholes in the cured acrylic coating. As such, inconsistent coverage and potential cracking of areas where the coating is applied too heavily are additional problems related to application of previous acrylic coatings.
In view of the current state of the art there is a continuing need for new and improved coating compositions that may be applied in-plant during manufacture of the roofing/siding membrane. In particular, a coating composition is needed that is reflective, energy efficient, as well as durable and easy to apply.